This invention relates to the driving efficiency of two motor/generators driven independently by single inverter.
Tokkai Hei 11-275826 published by the Japanese Patent Office in 1999 discloses a motor/generator which drives a plurality of rotors independently by applying a composite polyphase alternating current to a set of stator coils. The invention disclosed in Tokkai Hei 11-275826 is also disclosed in U.S. patent application Ser. No. 09/275,785 filed on Mar. 25, 1999 before the priority date of this invention and was granted as U.S. Pat. No. 6,049,152 after the priority date of this invention.
In the motor/generator disclosed in Tokkai Hei 11-275826, the composite polyphase alternating current with a fixed angular phase difference is supplied from an inverter to coils of each phase in the stator.
The research carried out by the present inventors has demonstrated that it is possible to drive two motors independently, if the rotors have a different number of magnetic poles, by connecting coils of the two stators to an inverter in parallel.
However with the above arrangement, the current for driving the rotation of one motor also flows in the coils of the other motor. When the number of magnetic poles in respective rotors is different, the current is actually ineffectual as it does not create a torque in the other motor. This increases copper loss in the motor.
It is therefore an object of this invention to suppress the generation of an ineffectual current generated when two motor/generators are driven independently by a single inverter.
It is a further object of this invention to control an induced electromotive force generated by the rotations of the motor/generator.
In order to achieve the above objects, this invention provides a motor/generator comprising a first motor/generator unit comprising a first rotor provided with a magnet and a first stator provided with a plurality of coils facing the first rotor, and a second motor/generator unit comprising a second rotor provided with a magnet and a second stator provided with a plurality of coils facing the second rotor.
The motor/generator is further configured as follows.
Providing that the number of coils in the first stator is S1, the number of pairs of magnetic poles in the magnet of the first rotor is P1, and the number of phases in a first alternating current which drives the first rotor through the coils of the first stator is M1, the coils of the first stator are divided into groups of the number of K1 satisfying the equation K1=S1/M1. The coils in each group of the first stator are mutually connected by either a Y connection or a delta connection.
Providing that the number of coils in the second stator is S2, the number of pairs of magnetic poles in the magnet of the second rotor is P2, and the number of phases in a second alternating current which drives the second rotor through the coils of the second stator is M2, the coils of the second stator are divided into groups of the number of K2 satisfying the equation K2=S2/M2. The coils in each group of the second stator are mutually connected by either a Y connection or a delta connection.
Providing that the groups of the first stator is numbered from 1 to K1/A, A being a natural number, the coils in each group of the first stator is numbered from 1 to M1, the groups of the second stator is numbered from 1 to K2/B, B being a natural number, the coils in each group of the second stator is numbered from 1 to M2, and i and j are natural numbers, a coil with a coil number j in a group number i of the first stator and a coil of a coil number i in a group number j of the second stator are connected to each other.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.